A perilymph fistula is a disorder of the auditory and vestibular system, which is caused by leakage of the perilymph existing in the inner ear tissues into the tympanic cavity (middle ear) through the inner ear windows (through either the round or oval window, or though both the round and oval windows), or through the fissura ante fenestram (which is a bone fissure located between the inner ear and the middle ear). Causes of this disease are considered to be congenital malformation, syphilis, stapes surgery, head injury (including barotraumas), sudden development (cryptogenic development), and the like. It has been known that perilymph fistulas are also caused by a drastic change in cerebrospinal fluid pressure or inner ear pressure, which is generated as a result of ordinary actions in our daily life, such as nose-blowing, sneezing, coughing, muscle straining, diving, climbing, or experiencing head trauma. This is a disease involving partial acute sensorineural deafness, vertigo, or disorder of balance.
Diagnosis of perilymph fistulas has conventionally been carried out by a method of comprehensively verifying physiological findings, symptoms, history of diseases, and other factors, in accordance with diagnostic standards (Asano et al., “Jiten (Prospects of Otolaryngology)” 34, 4; 1991, pp. 411-425). Accordingly, in many cases, the diagnosis is uncertain, and exploratory tympanotomy selected as a means for obtaining definite diagnosis has been problematic in terms of invasiveness to the patients. Moreover, there have been many cases where perilymph leakage cannot be confirmed by visual observation even when such exploratory tympanotomy is carried out, thereby resulting in a lack of definite diagnosis.
Sudden deafness is a type of acute sensorineural hearingloss, the cause of which cannot be specified, and it is a disease representing the highest percentage of instance among the various types of acute sensorineural hearingloss. It has been reported that as a result of tentatively performing exploratory tympanotomy on patients with sudden deafness, perilymph fistulas were observed in 8 out of 11 cases (Kunihide Yoshioka, “Jibiinkoka Tenbo (Prospects of Otolaryngology),” Vol. 26, Suppl. 6; 1983: pp. 517-539). Moreover, it has also been known that some patients with perilymph fistulas are misdaignosed as Meniere's disease, which is known as one cause of acute sensorineural hearingloss, and regarding which the number of the patients has increased in modern society. A report emphasizes the differential diagnosis between perilymph fistula an Meniere's disease based on the analysis of a large number of patients with this affliction. (D. C. Fitzgerald, “Ann. Otol. Rhinol. Laryngol.” 110; 2001: pp. 430-436). These facts show that perilymph fistulas are misdiagnosed as other diseases because the symptoms do not comply with the aforementioned diagnostic criteria. However, since a method for definite diagnosis of perilymph fistulas has not been established yet, the real picture is that it is still difficult to substantially identify the disease in the clinical setting. Thus, these problems have not yet been solved. Among various types of acute sensorineural hearingloss, the perilymph fistula is the only disease where disorders of the auditory and vestiblar system can be improved by operations, and prompt treatment greatly influences the cure rate thereof. Accordingly, it is strongly desired that a simple, reliable and low-invasive test for the diagnosis of perilymph fistulas to be developed.
To date, the following reports have been made: a report that proposes searching for a marker that can be used in diagnosis of perilymph fistulas and using ApoD and ApoJ as indicators (Thalmann et al., “Otolaryngology—Head and Neck Surgery,” 111, 3, 1; 1994: pp. 273-280); a report regarding an attempt to diagnose perilymph fistulas using GM1 (monosialoganglioside 1) as an indicator (Hitoshi Kanzaki et al., “Koseirodosho tokutei sikkan taisaku kenkyu jigyo/Kyusei kodo kanon nancho ni kansuru cyosa kenkyu han/Heisei 11 nendo hokokusho (Annual report 1999, by the Research project team regarding acute profound sensorineural hearingloss, Research project for specified diseases, the Ministry of Health, Labour and Welfare),” 2000: pp. 41-43); a report that proposes the use of prostagrandin D synthase as an indicator (G. Bachmann, et al., “J. Laryngol. Otol.” 115; 2001: pp. 132-135); a report regarding an attempt to diagnose perilymph fistulas using transferrin as an indicator (Rauch S. D., “Laryngoscope” 110(4); 2000: pp. 545-552); and so on. However, these techniques are not good enough for clinical applications.
COCH is a gene that has been identified as a causative gene of non-syndromic hereditary hearingloss DFNA9. A COCH protein encoded by this gene was designated “Cochlin” (N. G. Robertson, “Nature Genet.” 20; 1998, pp. 299-303; and NCBI OMIM home page, www.ncbi.nlm.nih.gov.
Focusing attention on the fact that Cochlin is an important protein with reference to human deafness, the present inventors have conducted a proteome analysis of Cochlin in bovine inner ear tissues, and have clarified that Cochlin has 3 different N-termini and that Cochlin exists as 3 types of isoforms, p63, p44, and p40, having molecular weights of 63 kDa, 44 kDa, and 40 kDa, respectively. In addition, the present inventors have reported that the LCCL module exists at the N-terminus (Trexler et al., “Eur. J. Biochem.” 267; 2000: pp. 5751-5757), that all mutations that have been discovered so far regarding DFNA9 are presented in this module, and that the mutations are contained only in the isoform p63, but not contained in the other isoforms (Ikezono et al., “Biochem. Biophys. Acta” 1535(3); 2001: pp. 258-265). However, with regard to the above report, a proteome analysis was only carried out via two-dimensional gel electrophoresis (2D-GE) on bovine inner ear tissues, and the clinical significance of Cochlin and the like has not been sufficiently studied.
N. G. Robertson et al. have produced an antibody to Cochlin, and have carried out immunological staining of inner ear tissues, so as to analyze the expression of Cochlin in the inner ear tissues (N. G. Robertson, “Hum. Mol. Genet.” 10(22): 2001: pp. 2493-2500). However, this report only describes analyses regarding localization of the protein in inner ear tissues or the like, and thus, there have been no findings regarding the existence of Cochlin in the perilymph.